Approximately 10 percent of all ovarian cancers are associated with autosomal dominant genetic predispostion. It is now well established that the great majority of these hereditary ovarian cancers are attributable to inherited mutations in the recently cloned and characterized tumor suppressor genes BRCA1 or BRCA2. The long-term goals of this project are to determine the molecular genetic mechanism through which BRCA-linked ovarian cancers develop and to define the clinical and biological features of these cancers. Specifically, this project will focus on two major aims, the first of which is to test the hypothesis that pathologically normal ovarian tissues from BRCA heterozygotes exhibit preclinical histologic, molecular genetic, and cell biological alterations. Ovaries removed prophylactically from women with deleterious germline BRCA mutations will be compared to those removed from women not at increased risk for ovarian cancer with regard to the prevalence of histological features that may represent premalignant alterations, and the ratio of proliferating to apoptotic epithelial cells. Using a combination of microdissection, PCR-based DNA analyses, and immunohistochemical techniques, ovaries from BRCA heterozygotes will be further analyzed for regional loss of the wild-type BRCA allele and TP53 mutation, the order in which these events occur, and the correlation of these events with regions of abnormal histologic variation. It is anticipated that these studies will lead to an improved understanding of the early molecular genetic events in heretidary ovarian tumorigenesis specifically, and to greater insight into the cell or region of origin of ovarian carcinoma generally. This information should prove useful in the development of new approaches for the early detection of ovarian cancer. The second major aim is to address the hypothesis that BRCA proteins function in the cellular response to therapeutic DNA damaging agents (chemical and physical), and further, to determine whether this function is specific for a particular type of DNA damage (e.g., double-strand DNA breaks). This aim will be accomplished by examining the effect of BRCA expression on the cellular response to several different classes of cytotoxic chemotherapeutic agents and radiation, using three experimental strategies for the comparison of BRCA-expressing and BRCA-nonexpressing cells: 1) conditional BRCA expression in BRCA-deficient human tumor cell lines; 2) direct comparison of BRCA-deficient and BRCA-wild-type tumor cell lines, and; 3) antisense-mediated BRCA depletion in BRCA-wild-type tumor cell lines. Data from these studies may lead to the development of more effective therapeutic strategies for genetically-defined subsets of ovarian cancer patients.